SEA  CAT  PROJECT

FINAL REPORT

 Feeding Ecology of the Sea Cat (Lontra felina) in Southern Chile.

1.            Introduction 

This report gives the most important final results of the scientific study, “Feeding Ecology of the Sea Cat (Lontra felina)”, supported principally by the International Otter Survival Fund - IOSF.  This research was undertaken between June 1999 and June 2000, in four study sites located approximately 42 km from Valdivia City in Southern Chile.

This study was realised with the aim of increasing the knowledge about the feeding ecology of L. felina and established the following hypothesis (H_o); the marine otter is not an opportunistic predator and thus the diet should not be strongly related with the environmental availability and consequently the prey selection should be more related to the calorific value of the prey than the environmental availability.

This work represents an important input in the knowledge of the sea cat diet, because it is the first that gives annual data and recorded seasonal variations in the diet.  Several studies about the diet of the marine otter have been made in Chile (Castilla and Bahamondes, 1979; Cabello, 1983; Ostfeld et al., 1989; Sielfeld, 1990; Medina, 1995a), however none of them carried out any annual work.  Partial results of this work were presented in the VIII International Otter Colloquium and in the Scientific Meeting organized by Universidad Austral de Chile in January and June 2001, respectively.

2.    General characteristics and basic information on the marine otter

 Some vernacular names of marine otter are; sea cat, Chilean sea otter, South American sea otter (English); chinchimén, chungungo (native name, Chile), huallaque (Perú), gato marino, gato de mar, nutria de mar (Spanish); loutra feline, loutre marine (French).

The Marine Otter, Lontra felina (Molina, 1872), belongs to the Mustelidae family and lives exclusively in marine habitats, especially exposed rocky shorelines (Ostfeld et al., 1989).  L. felina is distributed along the pacific coast between latitudes 6° (near Chimbote, Perú) and 56°S in Cabo de Hornos and Isla de los Estados (Orlog and Lucero, 1981).

For a long time this species has been the object of hunting, producing an important diminution in the population density.  For this reason, L. felina is classified as endangered in I.U.C.N's Red List of Endangered Species (Hilton-Taylor, 2000), as vulnerable in the Red Book of Chilean Terrestrial Vertebrates (Glade, 1993), and figures in the Appendix I of C.I.T.E.S. (Shouten, 1987).

The diet of L. felina is relatively well known.  It is mostly composed of invertebrates, crustaceans being the most important.  The consumption of molluscs such as gastropods, octopus and bivalves has also been described (Castilla and Bahamondes, 1979; Ostfeld et al., 1989; Sielfeld, 1990; Medina, 1995a).  Another food resource, but less important, are amphipods and isopods (Sielfeld, 1990).  When considering vertebrates, fish (predominantly from the families, Blennidae, Cheilodactylidae, Gobiesocidae, and Pomacentridae) are the most important food item (Castilla and Bahamondes, 1979; Ostfeld et al., 1989; Sielfeld, 1990).  Opportunistically and occasionally, L. felina may consume birds from the Phalacrocorax genus (Sielfeld, 1990).

However these studies have only been short-term surveys, thus nothing is known about the diet seasonality or the relationship between the diet composition, prey availability and energetic value of the main prey species.

 3.         Study area and methodology

 These results are based on the study carried out between June 1999 and June 2000.  Four study sites were selected on the basis of otter presence, access and observation possibility.  Accordingly, the selected sites were; Caleta Bonifacio, Bahía Curahuiche, Pilolcura and Punta Chungungo located between 39° 30’ S, 73° 00’ W and 38° 25’ S, 73° 00’ W (Figure 1). Study sites were visited for one day a month and observations were made during the day-time for 8 hours periods.  The total number of individuals observed in all the sites was 22.

Diet was assessed principally by faeces analysis and direct observation following the Estes classification (Estes, 1982).  Therefore, the size of prey species was determined by comparison with the size of an otter head.  Thus, when the prey was larger than the head of the otter, it was considered to be a large prey.  Between one half and the total length of the head size was medium prey and small when the prey was smaller than one half head size.  Taxonomic group, time and place where the prey was taken were identified by the help of 10 x 50 binoculars. The faeces were collected monthly in each study site.  The identification of the prey species was done using fish bones and pieces of the crustaceans that were consumed.

            The evaluation of the environmental availability was done monthly, using fish and crab traps.  These were employed approximately 40 meters from the shoreline at 15 meters depth for 24 hours.  All the captures were standardised, in this manner the environmental availability was estimated by number of individuals per hour of trapping (indv/hr). The energetic evaluation of the most important species of crustaceans consumed was made in a calorimetric bomb and was standardized in Kcal/gr of dry weigh.

    Figure 1.  Study sites located, between 39° 30’ S, 73° 00’ W and 38° 25’ S, 73° 00’ W 

          Bonifacio,      Bahía Curahuiche,     Pilolcura       Punta Chungungo.

 4.                 Results  

Diet and environmental availability

The main prey species that composed the diet of L. felina were identified and seasonal variations of the diet and prey availability were recorded.  Equally, the relationship between the calorific value of the main prey and their preference, were evaluated.

According to the data, in the studied environment the diet of L. felina was composed of 25 species.  Of these, 13 species were crustaceans, 10 fishes and 2 corresponded to molluscs.  No seasonal difference either in number of prey species or diversity was recorded (Figure 2).

Furthermore, 78.41% were crustaceans, 20.17% were fishes and 1.42% were molluscs.  Coincidentally, the frequency of capture showed that environmental availability  was made up of 93.25% crustaceans and 6.75% fishes.  

  Both diet and environmental availability showed seasonal differences, with a high correlation between them.  Thus, the seasonal change in the species availability was clearly reflected in prey consumption, in this manner species like the crab Taliepus dentatus was principally eaten all the year and equally was this species the most frequently captured by the traps.  Nevertheless, during spring a change in the captures was recorded, the crab Cancer edwardsi being the most abundant species in the environment.  This change was equally observed in otter diet, because in this season the prey species mostly consumed was C. edwardsi .

Prey Size

According to the data recorded during the year, L. felina showed a high consumption of medium (3.8 cm to 7.6 cm) and large (> 7.6 cm) prey species in relation to their head size .

Crustaceans consumed and energetic value.

The frequency of the crustacean consumption was compared with the energetic values (Kcal/dry weigh).  No direct relation between frequency of consumption and energetic value was observed.

In this manner, species such us T. dentatus, was predominantly consumed all the year but their calorific contribution was very low (2.56 Kcal/gr. dry weigh), compared with other species such us O. punctatus (4.91 Kcal/dry weigh) and C. setosus (3.17 Kcal/gr. dry weigh) (Figure 10).

4.                 Discussion

 The results obtained suggest that the research hypothesis should be rejected.  This is because, in the studied environment, the marine otter (Lontra felina) behaves like an opportunistic predator, as throughout the year the main prey species consumed by the otter correlate highly with the prey species available, a relationship that was observed in all the seasons.

Moreover, the otters showed no positive relation between calorific value and the frequency of consumption of the main prey species consumed.

For these reasons, as expected, it is possible to confirm that in Southern Chile L. felina is principally a crustacean feeder (> 78%).  Thus the present results are similar to those registered in Chiloé Island, for coastal regions from central Chile and the observations communicated previously for sites near to these study sites (Cabello, 1983; Ostfeld et al., 1989; Medina 1995a).

Compared with other species of otters the feeding ecology of L. felina is closer to Aonyx capensis, Lutra maculicollis and Lutra perspicillata (Houssain and Choudhury, 1998; Perrin and Corugati, 2000) and more different from Enhydra lutris and Lutra lutra in marine environments (Estes et al., 1982, Estes, 1989; Kruuk and Hewson, 1978; Kruuk and Moorhouse, 1990; Kruuk, 1995).

Finally, these results suggest that the most profitable prey species for L. felina are represented by species with the highest environmental availability which they can catch more easily and not necessarily the preys that offer a high calorific value.  In this perspective, it seems to be that the energetic compensation is more a quantitative than qualitative process, and this my help us to understand why the L. felina spend the major part of their time budget on feeding. (Castilla and Bahamondes, 1979; Medina, 1995b; Bartheld, 2001).

 6.         Conclusions 

i)                    According to the results in the studied sites, the Marine Otter (Lontra felina) was an opportunistic predator. 

ii)                  The diet of L. felina was highly related to the preys available in the environment.   

iii)                The diet was principally composed of crustaceans.  

iv)                Seasonal variations in the otter diet were coincident with seasonal variations in the prey availability.

 v)                  Lontra felina showed more consumption of the more available preys species than the high calorific value preys.

 7.         Needs and research priorities

             The outcome of this research gives us much information about the feeding ecology of L. felina.  However, many problems and questions are still waiting to be answered. Thus, we have a lot of work for the future.  This work will firstly be focused to determinate the population density all along the seashore of Chile, to asses the home range and the role of the marine otter in the structure of the inter-tidal community.

Another important question will be the human dimension of the marine otter conservation problem.  For this we will need to map the distribution of threats using geographic information systems to assemble the density distribution data.

Finally, in this manner, we can obtain the best approximation to encourage and identify the best places in the country, to develop conservation programs in the different levels proposed by the Otter Specialist Group and discussed in the last Otter Colloquium realised in Chile. 

 Bibliography

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Cabello, C. C. (1983).  La nutria de mar en la Isla de Chiloé.BoletínTécnico CONAF., 6, 1-37.

 Castilla, J. C. (1976).  Guía par la observación del litoral. Expedición a Chile.,118pp.

Castilla, J. C. & Bahamondes, I. (1979).  Observaciones conductuales y ecológicas sobre Lutra felina. (Molina) 1782 (Carnivora: Mustelidae) en las zonas central y centro-norte de Chile.  Arch. de Biol. y Med. Exp., 12, 119 – 132. 

CONAF (1993).  Libro rojo de los vertebrados terrestres de Chile (Glade, A, Ed.). Corporación Nacional Forestal, Ministerio de Agricultura, República de Chile. 65 pp.

Estes, J. A., Jameson, R. J. & Rhode, E. B. (1982).  Activity and prey selction in the sea otter: influence in population status on community structure. Am. Nat., 120, 242 – 258. 

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 Hilton–Taylor, C. (2000).  IUCN Red List of Threatened Species. IUCN, Gland, Switzeland. UK., 61 pp. 

Houssain, S. A. & Choudhury, B. C. (1998).  Feeding ecology of the smooth-coated otter Lutra perspicillata in the National Chambal Sanctuary, India., 229 – 249. En:  Dunstone, N. y Gorman, M. (1998) Behaviour and Ecology of Riparian Mammals.Cambridge University Press., 391 pp. 

Kruuk, H. & Hewson, R. (1978).  Spacing and foraging of otters (Lutra lutra) in a marine habitat, J. Zool., London, 185, 205-12. 

Kruuk, H. & Moorhouse, A. (1990).  Seasonal and spatial differences in food selection by otters (Lutra lutra) in Shetland. J. Zool. London, 221, 621-637. 

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Molina, J. I. (1782).  Saggio sulla storia naturale del Chili, del signor abate Giovanni Ignazio Molina. Stampeeroa del S.Tomaso d’Aquino,Bologna. 367 pp.   

Ostfeld, R. S., Ebensperger, L., Klostermand L., & Castilla, J. (1989).  Foraging, activity budget, and social behaviour of the South American marine otter Lutra felina (Molina 1782). National Geographic Research., 5, 422 – 438. 

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 Photographs  

 Photograph 1.  Adult of Lontra felina sleeping on rock near the shore.

 Photograph 2.  Two adult sea cats playing on a rock covered by             brown  seaweed . 

         Photograph 3.  Adult sea cat swimming among kelp (Macrocystis          pyrifera). 

                         Photograph 4.  Sea cat cub into the funnel on the seashore.  

 Photograph 5.  Studied sites. All of these correspond to exposed rocky seashore.

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